The invention relates to a recording material for the ink-jet printing process.
The ink-jet recording method is used to produce color graphics, full-color copies and also for text printings, so it covers a very wide field of applications. The recording material must fulfill various requirements are made of this recording material, such as high gloss, good drying, high color density, good wet rub-off properties, low mottle, and high water fastness.
The ink-jet recording method is used to produce color graphics, full-color copies and also for text printings, so it covers a very wide field of applications. The recording material must fulfill various requirements that are made of this recording material, such as high gloss, good drying, high color density, good wet rub-off properties, low mottle, and high waterfastness.
High-performance ink-jet printers for producing photographic-quality printings use inks with a high water content as solvent. In addition, the ink application volume by these printers is greater than that with traditional ink-jet printers. Films were initially used as ink-receiving materials, because they are characterized by a high dimensional stability when wetted with water, but they have poor drying properties. One possibility of producing glossy, photographic-quality ink-jet printings is the use of resin-coated papers that are provided with an ink-receiving layer. DE 19 618 607 A describes the use of polyolefin-coated papers to achieve high gloss values. However, the long drying time of these papers is a disadvantage, because with this material the ink fluid cannot be diverted into the paper support. The resin coating acts as a barrier layer with respect to the ink fluid.
The object of the invention is to provide a recording material for the ink-jet printing method, which provides images with a high color density, good wet rub-off fastness, good water fastness, low mottle and beyond that rapid drying after printing with aqueous ink and high gloss.
This object is achieved by a recording material which comprises a raw base paper, a layer containing polyvinyl alcohol (PVA) extruded on the raw base paper, and an ink-receiving layer applied from an aqueous dispersion or solution.
The recording materials according to the invention show a very good adhesion of the PVA layer on the raw base paper, brilliant gloss after calendering or treatment in a chill roll and excellent drying properties after printing with aqueous inks. The drying properties are particularly improved in view of ink-jet recording materials which have a polyolefin layer formed on the paper support. A pretreatment of the raw base paper in order to improve adhesion of the PVA layer on the raw base paper by corona treatment or flame treatment or applying a separate adhesive layer between the paper and the PVA layer is not necessary.
Polyvinyl alcohols which may be used according to the invention are all polyvinyl alcohols which are extrudable or which are made extrudable by the addition of appropriate additives such as plasticizers. Polyvinyl alcohols which may be used according to the invention are in particular polyvinyl alcohol homopolymers, polyvinyl alcohol copolymers and/or mixtures thereof. Suitable PVA copolymers are in particular those which contain ethylene and/or vinyl acetate as polymerizable monomers.
According to a preferred embodiment of the invention, the polyvinyl alcohol is hydrolyzed to an extent of 75 to 99 mol %, and it may have a degree of polymerisation of 200 to 2500. The melt flow index (MFI) of the polyvinyl alcohol resins to be used according to the invention may be 10 to 50 g/10 minutes, preferably 20 to 30 g/10 minutes. The extruded layer containing polyvinyl alcohol may contain 5 to 95 wt % of the extrudable polyvinyl alcohol.
Additives which improve the extrusion properties of the polyvinyl alcohol are, for example, plasticizers. A plasticizer may be incorporated into the polymer matrix during the preparation of the polyvinyl alcohol or may simply be added to the extruder and mixed therein with the polyvinyl alcohol. Suitable plasticizers are all PVA compatible plasticizers such as hydrophylic plasticizers. Suitable plasticizers are in particular polyhydric alcohols, such as glycerol, polyethylene glycol, ethylene glycol, diethylene glycol and mannitol. The plasticizer or a plasticizer mixture containing several plasticizers may amount to 1 to 30 wt %, preferably 5 to 20 wt %, based on the weight of the extrusion coated layer.
Polymers or copolymers which may be included in the layer which is extruded on the raw base paper may contain, for example, polyurethanes, polyolefins, ethylene copolymers, polyalkylene oxides, such as polyethylene oxyethanol, polycarbonates, polyesters, polyamides and polyesteramides.
The PVA layer extruded on the raw base paper may contain those additives which are usually contained in the polyolefin coating of photobase papers. These are in particular white pigments, color pigments, colorants, fillers, optical brighteners and phosphoric acid which is used to improve thermal stability of PVA. A conventional white pigment is titanium dioxide. Further fillers and pigments are calcium carbonate, ultramarine, cobalt blue, carbon black, alumina and silica. In particular, silica is useful for shortening the time required for drying of the ink.
The coating weight of the extruded layer may be 10 to 60 g/m2, preferably 20 to 40 g/m2. The extrusion on the raw base paper is performed according to methods which are known to the skilled worker in the paper manufacturing industry. The extruder is, for example, a screw extruder. According to a preferred embodiment of the invention, the temperature in the extruder or the temperature in different sections of the extruder is adjusted to 140 to 230xc2x0 C., in particular 160 to 180xc2x0 C. In particular, in a two-inch extruder it is preferred to compound the resins and further optional additives with screw speeds of more than 50 rpm, in particular more than 75 rpm, and to extrude the resulting mixtures. If an extruder other than a two-inch extruder is used, it is preferred to adjust the screw speed in such a way that the viscosity of the material to be extruded corresponds to the viscosity of a material which is compounded and extruded in a two inch screw extruder at screw speeds of more than 50 rpm and a temperature of 140 to 230xc2x0 C.
In order to achieve high gloss it is preferred to use a high gloss chill roll. Very good gloss results are also obtained with the chill rolls of DE 198 12 445.
As support material any kind of raw base paper may be used. Preferably surface sized papers, calendered or non-calendered papers or highly sized raw base papers may be used. The raw base paper may be sized with acidic or neutral sizing agents. Especially suitable are papers with a surface roughness of less than 300 Sheffield units determined according to Tappi T538 roughness. The raw base paper shall have a high dimensional stability and should be able to absorb the water which is contained in the ink without formation of curl. Papers with a high dimensional stability which are manufactured from pulp mixtures, comprising softwood sulphate fiber pulp and eucalyptus pulp are particularly suited. The disclosure of DE 196 02 793 B1, which discloses a raw base paper for a ink-jet recording material, is incorporated herein by reference.
According to a preferred embodiment the raw base paper is not too strongly sized in order to allow a paper surface with an open pore structure. Particularly preferred papers are those having a roughness of less than 200 Sheffield units. The basis weight of the raw base paper may be 60 to 250 g/m2.
The raw base paper may contain further additives which are conventional in the paper manufacturing industry such as colorants, optical brighteners, pigments, and defoaming agents. It is also possible to use waste pulp and processed recycled paper.
Onto the extruded PVA layer any known ink receiving layer may be applied from an aqueous phase, for example, by means of a blade or a coating knife. The ink receiving layer may be applied as a single layer or multiple layers. The ink-receiving layer may contain inorganic and/or organic pigments such as titanium dioxide, silica, alumina, calcium carbonate, boehmite, bentonite, polyamide, polyesters, polyolefins and olefin copolymers. Preferably, no pigments are used in the ink-receiving layer. If the ink-receiving layer shall contain pigments, the amount of pigments should not exceed about 10 wt %, based on the weight of the dry ink-receiving layer in order not to adversely affect the gloss of the image. If nano-sized pigments with an organic coating are used in the ink-receiving layer their amount may exceed 10 wt %. Additionally, the ink-receiving layer may contain a hydrophilic binder, such as a water soluble polyvinyl alcohol, dye fixing agents, colorants and optical brighteners.
Surprisingly, it was found that by applying the ink-receiving layer as an aqueous dispersion or aqueous solution, the adhesion of the extruded PVA layer to the paper is distinctly improved. It is assumed that the adhesion is improved because of the migration of water into the PVA layer and the softening of the polyvinyl alcohol at the border layer of the paper and the subsequent drying process. The coating weight of the ink-receiving layer may be 0.1 to 10 g/m2, preferably 1 to 2 g/m2.
In order to adjust curl, antistatic properties and feed properties in the printer, on the back side of the raw base paper there may be provided a separate function layer. Especially suitable back side layers are described in DE43 08 274 A1 and DE 44 28 941 A1 which are incorporated herein by reference.
The following examples shall further explain the invention.
Raw base papers were produced as follows:
A paper with a basis weight of 83 g/m2 and a Thickness of 87 xcexcm was produced on a Fourdrinier paper machine. The pulp used had a degree of beating of 29 according to Schopper-Riegler. The pulps used were approximately 42 wt % pine kraft pulp and approximately 54 wt % eucalyptus pulp. In addition, 4 wt % clay was added as pigment. The sizing agent added was 0.1 wt % alkylketene dimer (Aquapel(copyright) C526) and 0.05 wt % starch, and the wet strength agent was 0.5 wt % poly(aminoamide)-epichlorohydrin resin (Kymene(copyright) 617 HP). A 7.0 wt % polyvinyl alcohol solution (Moviol(copyright) 10-98) was used as surface sizing agent. The paper had a roughness of 98 according to Sheffield.
A paper with a basis weight of 130 g/m2 and a thickness of 138 xcexcm was produced on a Yankee machine. The pulps had a degree of beating of 27 according to Schopper-Riegler. Approximately 24.5 wt % pine kraft pulp and approximately 67 wt % eucalyptus pulp were used as pulp. Clay was added in an amount of 8.5 wt % as the pigment. The sizing agent added was 0.055 wt % alkylketene dimer (Aquapel(copyright) C526) and the wet strength agent added was 0.6 wt % poly(aminoamide)-epichlorohydrin resin (Kymene(copyright) 617 HP). For the surface sizing, a 1.97 wt % Emox(copyright) TSC starch solution was used. The paper had a roughness of 120 according to Sheffield.
A paper with a basis weight of 174 g/m2 and a thickness of 167 xcexcm was produced on a Fourdrinier paper machine. The pulps had a degree of beating of 30 according to Schopper-Riegler. The pulps used included 31.25 wt % maple kraft pulp and 68.75 wt % mixed short-fiber hardwood kraft pulp. The sizing agents added were 0.446 wt % alkylketene dimer (Aquapel(copyright) C526) and 1.32 wt % starch, and the wet strength agent was 0.326 wt % poly(aminoamide)-epichlorohydrin resin (Kymene(copyright) 617 HP). A 6.0 wt % Emox(copyright) TSC starch solution was used for surface sizing. This paper had a roughness of 200 according to Sheffield.
A paper with a basis weight of 136 g/m2 and a Thickness of 147 xcexcm was produced on a Fourdrinier paper machine. The pulps had a degree of beating of 33 according to Schopper-Riegler. The pulp used was 13.0 wt % maple kraft pulp and 87.0 wt % mixed short-fiber hardwood kraft pulp.
The sizing agent added was 0.64 wt % starch and 0.64 wt % stearate. A 6.0 wt % Emox(copyright) TSC starch solution was used for the surface sizing. The paper had a roughness of 155 according to Sheffield.
The amounts given for the weight of the pulps and pigments are based on the pulper furnish of these substances; the amounts given for the weight of sizing agents and wet strength agents are based on the dry fiber content.
The ink-receiving layer applied in Examples 1 to 8 was applied as an aqueous dispersion which is subsequently dried by conventional means. This ink-receiving layer had the following composition:
The weight amounts are based on the dried layer. The ink-receiving layer can be applied with all conventional coating methods.